Magnetic governor drive coupling

ABSTRACT

A drive assembly for connecting a governor (10) to an engine (12) for absorbing torsional vibrations in the shaft while providing a direct drive between the engine and the governor during overtravel. The drive assembly includes a shaft (16) driven by the engine (12) and a rotor (24) mounted on the end of the shaft and received within a housing (18) mounted for rotation about the shaft. The housing contains magnets (35 and 37) which interact with magnetically permeable portions of the rotor (24) to establish a magnetic flux coupling therebetween. During operation, torsional vibrations in the drive shaft (16) will tend to rotate the rotor (24) relative to the housing (18), thereby reducing the torsional vibration imparted from the engine (12) to the governor (10). Pins (32 and 34) limit the amount of relative movement between the rotor and the housing so that the rotor engages the pins, providing the direct drive to the governor during overtravel. The housing includes a gear (20) mounted about its circumference for driving a pinion (22) leading to the governor (10).

TECHNICAL FIELD

This invention relates to a drive assembly for a mechanical element and,more particularly, to an improved drive from an engine to an associatedgovernor.

BACKGROUND ART

Often there is a significant amount of torsional vibration in a drivetrain leading from an engine, as a diesel engine, to its governor.Excessive torsional vibrations adversely affect the operation of thegovernor which in turn causes the engine to operate erratically. Theoscillatory vibrations in the governor drive must be reduced oreliminated for satisfactory governor and engine operation.

Various mechanical linkages have been proposed in an attempt to reduceor eliminate the torsional oscillations between the drive train and theengine governor. However, direct drive systems with a plurality of gearsusually experience the problem referred to as backlash, which resultsfrom machining tolerances allowing for imperfectly located gear centersand machined gear tooth profile. Backlash causes undesirable torsionalvibrations, and the problem becomes more significant as the number ofgears in the drive is increased and as the drive and power or loadrequirements change. Moreover, a mechanical drive specifically designedfor driving a governor with no torsional vibrations in one engine maynot be useful for other engines or their applications.

DISCLOSURE OF INVENTION

In one aspect of the present invention, a drive assembly is provided fordriving a mechanical element from a drive shaft having a rotor mountedon one end thereof. The assembly has a housing mounted for rotationabout the shaft with the rotor being enclosed in the housing. Members,as pins or stops, are provided for permitting only a selected degree ofrelative rotational motion between the rotor and the housing. A fluxcoupling established between the magnetic elements and the rotor alignthe rotor between the stops or pins during rotation. Only a selecteddegree of relative rotational motion between the rotor and the housingduring rotation of the drive shaft is permitted by the placement of thestops. The housing is provided with means for driving the mechanicalelement.

According to the present invention, a drive assembly employs, in part, amagnetic coupling to reduce the torsional oscillations between an engineand its governor. In the event that the amplitude of the vibration fromthe drive train to the governor exceeds an established angulardisplacement of the magnetic coupling, as during overtravel, a positivedrive from the engine to the governor is provided until the amplitude ofthe vibration decreases to a level less than the established angulardisplacement of the coupling.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view, partly in schematic form, of a driveassembly in accordance with an embodiment of the present invention.

FIG. 2 is an exploded perspective view of the drive assembly shown inFIG. 1.

FIG. 3 is a cross-sectional view of the drive assembly of FIG. 2.

FIG. 4 is an end view of the drive assembly shown in FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1 of the drawings, governor 10 is coupled to engine 12by drive assembly 14. A housing 18 is mounted for rotation about shaft16 and has an annular gear 20 for driving pinion 22 and thereby governor10. As will be discussed in detail below, variations in the amplitude ofthe torsional vibrations on shaft 16 are not imparted to pinion 22 aslong as the amplitude is less than a selected amount. However, if theamplitude of the torsional vibrations exceeds the selected amount asestablished by an angular displacement of a magnetic coupling withinhousing 18, a direct drive connection is provided to governor 10 fromengine 12.

Torsional vibrations in the drive shaft tend to rotate the rotorrelative to the housing. These vibrations are resisted by the fluxcoupling between the rotor and the magnets. The resistive magnetic forceof the flux coupling tends to become greater as the gap between therotor and housing decreases. The magnetic flux density variesproportionately with the angular displacement of the rotor relative tothe housing. Thus the varying magnetic flux density of the magneticcoupling, which is proportional to torsional amplitude, acts as amagnetic spring between the rotor and housing. Stops are necessary toprevent overtravel which would allow contact of the rotor and housingand for providing direct drive when the angular displacement of themagnetic coupling is exceeded.

Referring to FIGS. 2-4, the drive assembly 14 will now be described. Ametal rotor 24, which may be in the form of a bar-shaped rotor, issuitably attached to drive shaft 16. The rotor 24 has opposed outwardlyextending flanges 26 and 28 which are made of magnetically permeablematerial, such as soft iron, ceramic magnets, and the like. Althoughonly two opposed flanges are shown, it will be apparent that the numberof projections, as flanges 26 and 28, are selected in accordance withthe desired configuration of the magnetic coupling. The rotor 24 isreceived and retained within housing 18 by bearing 30.

Housing 18 is mounted for rotation about shaft 16 and has spaced-apartstop pins 32 and 34 secured in an end wall 33. The pins 32 and 34 aresubstantially parallel to each other and to the axis of shaft 16 andform an angle θ therebetween wherein the vertex of the angle iscoincident with the axis of shaft 16. The magnitude of angle θ isselected in accordance with the circumferential width W of the flange 26(FIG. 4), thereby defining the selected angular displacement of therotor 24 with respect to the housing 18.

Housing 18 has fixed therein two similar arcuately-shaped magnets 35 and37 facing each other within the housing and defining gaps or spaces 36and 38 therebetween. The magnets are arranged so that a magneticpolarity exists on one side of each space 36 and 38, and an oppositemagnetic polarity exists on the other side of each said space 36 and 38to provide a magnetic field having lines of magnetic flux therebetween.As a result of the flux coupling, flange 26 on the rotor 24 tends toalign itself across the space or gap 36, and flange 28 tends to alignitself across the space or gap 38. This alignment is hereinafterreferred to as the rest position. The flanges 26,28 of the rotor may bemade of magnetically excitable metal (soft iron) or may be magneticmaterial, such as a ceramic magnet, which will have poles opposite tothe adjacent poles on the magnets 35,37, such that the poles on themagnets 35,37 are magnetically opposite to the magnetic poles on therotor to attract each other in coupling relationship.

A cover 40 is retained in housing 18 by a snap ring 42, thereby definingan enclosed volume within the housing which can be filled with a liquidif desired. The liquid can be of many forms including a suspension ofmagnetic particles for improving the damping characteristics between therotor and the housing.

INDUSTRIAL APPLICABILITY

The operation of the drive assembly 14 will now be described. Engine 12imparts vibrational energy to shaft 16 and rotor 24 rotates with respectto housing 18, but said rotation is resisted by the magnetic flux actingon rotor 24. As the rotational position of the rotor 24 relative to thehousing 18 increases from the rest position, the flux couplingtherebetween becomes stronger, tending to reduce torsional vibrationsbetween drive shaft 16 and gear 20. When housing 18 and shaft 16 arerotating at the same speed and there is no vibrational energy imparted,rotor 24 is in the rest position.

Assuming that the shaft 16 is rotating in a clockwise direction fromstartup, flange 26 on rotor 24 may engage stop pin 32 if the magneticflux density is insufficient to retain flange 26 between pins 32 and 34.As the speed of the shaft becomes more closely equal to that of thehousing, the magnets 35 and 37 tend to align the flanges 26 and 28 onthe rotor 24 so that the flanges are located between pins 32 and 34.This permits the torsional vibration to be absorbed by the relativemovement of the flange 26 between the pins 32 and 34. If the vibrationsare of large amplitude, flange 26 will engage either pin 32 or 34 thusprovided a direct mechanical link between the engine 12 and the governor10 and preventing the rotor from contacting the housing due toovertravel.

It is apparent that although only one set of pins is shown, a second setof pins could also be provided on each side of flange 28. Moreover, itis apparent that the pins 32 and 34 need not necessarily be equallyspaced from the edges of gaps 36 and 38. If the pins are unequallyspaced with respect to the end portions of gap 36 or gap 38, theassembly will absorb larger torsional vibrations in one direction thanin the other. It is also apparent that the larger torsional vibrationsare damped as the angle θ is increased.

Other aspects, objects and advantages of this invention can be obtainedfrom a study of the drawings, the disclosure and the appended claims.

What is claimed is:
 1. A drive assembly for driving a mechanical elementfrom a drive shaft comprising:a drive shaft (16); a rotor (24) mountedon an end of the shaft and having two portions of magnetically permeablematerial thereon; a housing (18) mounted for rotation about said shaft,said housing encircling said rotor; pin means (32,34) carried by saidhousing (18) and positioned on opposite sides of said rotor (24) forpermitting only a selected degree of relative rotational motion betweensaid rotor and said housing; magnet means (35,37) for aligning saidrotor (24) between said pin means (32,34), said magnet means includestwo arcuately-shaped magnets (35,37) carried by said housing, eachmagnet having two concentrically-shaped faces, a front and a rear face,and two end faces, the end faces of one of said magnets being spacedfrom the end faces of the other of said magnets to define spaces (36,38)therebetween, said portions of magnetically permeable material on saidrotor aligning with said spaces (36,38) between said magnet means(35,37); and means (20) on said housing for driving said mechanicalelement.
 2. A drive assembly for driving a mechanical element from adrive shaft comprising:a drive shaft (16); a rotor (24) mounted on anend of the shaft and having opposed flanges (26,28) thereon; a housing(18) mounted for rotation about said shaft, said housing encircling saidrotor; pin means (32,34) carried by said housing (18) and positioned onopposite sides of said rotor (24) for permitting only a selected degreeof relative rotational motion between said rotor and said housing;magnet means (35,37) for aligning said rotor (24) between said pin means(32,34), said magnet means includes two arcuately-shaped magnets (35,37)carried by said housing, each said magnet having planar end faces withthe end faces on one of said magnets lying parallel to and being spacedfrom the end faces on the other of said magnets and defining spaces(36,38) therebetween; and said opposed flanges (26,28) on said rotoraligning with said spaces (36,38) between said end faces of the magnetmeans (35,37) during rotation of said drive shaft (16) and said housing(18).
 3. The drive assembly of claim 2 wherein at least one of saidflanges (26,28) engages at least one of said pins (32,34) when torsionalvibration exceeds a selected amount.
 4. A drive assembly for driving amechanical element from a drive shaft comprising:a drive shaft (16); arotor (24) mounted on an end of the shaft and having opposed flanges(26,28) thereon; a housing (18) mounted for rotation about said shaft,said housing encircling said rotor; pin means (32,34) carried by saidhousing (18) and positioned on opposite sides of said rotor (24) forpermitting only a selected degree of relative rotational motion betweensaid rotor and said housing; magnet means (35,37) for aligning saidrotor (24) between said pin means (32,34), said magnet means includestwo arcuately-shaped magnets (35,37) carried by said housing, each saidarcuately-shaped magnet having planar end faces on the opposite endsthereof, the end faces of said magnets being spaced from each other anddefining spaces (36,38) therebetween; and each said opposed flange(26,28) on said rotor aligns with one of said spaces (36,38) betweensaid end faces of said magnet means during rotation of said drive shaft.